Answer Key for Exam B 2 points each Choose the answer that best completes the question. Read each problem carefully and read through all the answers. Take your time. If a question is unclear, ask for clarification during the exam. Mark your answers on the scantron sheet and on your copy of the exam. Keep your copy of the exam and check your grade with the posted answers on the course website and the grade posted on D2L. You will have 1 week to ask for corrections. 1. The Exam Version listed at the top is: (a) Version A (b) Version B (c) Version C (d) Version D 2. What does the Hubble tuning fork illustrate? (a) the evolutionary sequence of galaxies (b) the motions of galaxies (c) the locations of galaxies (d) aclassificationscheme 3. Which of the following galaxies can be found with a bar-like structure in them? (a) spiral (b) irregular (c) elliptical (d) all of the above 1 4. What ionizes the gas in a planetary nebula (see the image below) and makes it visible? (a) X-ray photons emitted by a pulsar (b) ultraviolet photons emitted by the stellar core (c) the shock wave from a supernova (d) hydrogen burning in the nebular gas 5. Which point on the figure below represents the location on the H-R diagram where the star is expelling mass creating a planetary nebula? (a) A (b) C (c) B (d) D 6. Neutron stars are supported by (a) Ordinary thermal pressure supplied by the energy from nuclear reactions (b) Quantum mechanical pressure of relativistic electrons (c) Quantum mechanical pressure of non-relativistic neutrons (d) The nuclear force 2 7. You observe a supernova spectrum with strong Balmer Lines. It means you are seeing (a) SN Ia (b) Nova (c) Core Collapse (d) Can not tell 8. On the main sequence a 3 M star creates energy using: (a) the CNO cycle (b) the p-p cycle (c) the triple alpha process (d) gravitational contraction 9. is the result of mass distorting the fabric of spacetime. (a) Energy (b) Fusion (c) Radiation (d) Gravity 10. According to Hubble’s law, as the distance of a galaxy its increases. (a) increases; luminosity (b) decreases; luminosity (c) increases; recessional velocity (d) decreases; recessional velocity 11. Stars less than 8 M will end up as: (a) helium white dwarfs (b) neutron stars (c) carbon/oxygen white dwarfs (d) black holes 12. Novae occur because (a) runaway thermonuclear fusion of hydrogen on the surface (b) the hydrogen has time to cool and is supported by quantum mechanical pressure of electrons (c) Carbon and Oxygen fusion runs away in the center (d) both (a) and (b) 3 13. A low-mass main-sequence star’s climb up the red giant branch is halted by: (a) the end of hydrogen shell burning. (b) the beginning of helium fusion in the core. (c) quantum mechanical pressure in the core. (d) instabilities in the star’s expanding outer layers. 14. The most likely dark matter candidate seems to be: (a) black holes (b) neutron stars (c) planets (d) neutrino-like particles (e) super symmetric matter 15. Helium burns in the core of a horizontal branch star via and produces . (a) the triple-alpha reaction; carbon and oxygen (b) the triple-alpha reaction; oxygen and neon (c) the proton-proton chain; lithium (d) the proton-proton chain; iron 16. The Type II supernova that created the Crab Nebula (image below) was seen by Chinese and Arab astronomers in the year A.D.1054. Because the star is 6,500 light-years away from us, we know the star exploded in the year: (a) A.D. 7554. (b) A.D. 1054. (c) 5446 B.C. (d) 7554 B.C. 4 17. Nearly all the Carbon in the Universe is produced in (a) Core collapse supernovae (b) Type Ia supernovae (c) All types of supernovae (d) during CNO burning 18. Pulsars are the result of (a) the rotation of a neutron star with a strong magnetic field (b) core collapse supernovae (c) little green men (d) we have no idea 19. An iron core cannot support a massive main-sequence star because iron: (a) has poor nuclear binding energy. (b) cannot fuse with other nuclei to produce energy. (c) supplies too much pressure. (d) fusion only occurs in a degenerate core. 20. Which star spends the least time as a main-sequence star? (a) 0.5 M (b) 3 M (c) 1 M (d) 10 M 21. You observe a supernova spectrum with no Balmer lines, but a strong Silicon line with absorption at 6150 A.˚ It means you are seeing (a) SN Ia (b) Nova (c) Core Collapse (d) Can not tell 22. The energy for solar activity comes from (a) Radiation (b) Magnetic Fields (c) Convection (d) Conduction 5 23. White dwarfs are supported by (a) Ordinary thermal pressure supplied by the energy from nuclear reactions (b) Quantum mechanical pressure of relativistic electrons (c) Quantum mechanical pressure of non-relativistic neutrons (d) The nuclear force 24. We can determine how the density changes with radius in the Sun using: (a) radar observations. (b) high-energy (gamma ray) observations. (c) neutrino detections. (d) helioseismology. 25. Stars reach the Zero Age Main Sequence (ZAMS) when: (a) They start burning helium in their cores (b) They cross the birth line (c) They start burning hydrogen in their cores (d) They start burning hydrogen in a shell 26. What is the radius of the event horizon of a 10 solar mass black hole? (a) 3 km (b) 30 km (c) 10 km (d) 100 km 27. The maximum mass of a neutron star is: (a) The Chandrasekhar mass (b) At least 2.2 M (c) Not completely certain, since we haven’t yet solved nuclear physics (d) both (b) and (c) 6 28. Normally, muons created by cosmic rays at high altitudes decay in a very short time, a time so short that they should not reach the ground. From the figure below, which muon is most likely to be detected on the ground? (a) muon A (b) muon B (c) muon C (d) muon D 29. Besides shape, what characteristic clearly separates elliptical galaxies from spiral galax- ies? (a) size (b) age (c) shape (d) color 30. The property of a star that determines its destiny is its: (a) density (b) radius (c) luminosity (d) mass 7 31. The solar cycle is the result of (a) Convection (b) Winding up of the solar magnetic field (c) Di↵erential rotation (d) Both (b) and (c) 32. If the Sun were to be instantly replaced by a 1 M black hole, the gravitational pull of the black hole on Earth would be: (a) much greater than it is now. (b) the same as it is now. (c) much smaller than it is now. (d) irrelevant because Earth would be quickly obliterated by the strong tidal force of the black hole. 33. The bulk of neutron stars are made of (a) neutrons of course (b) iron (c) neutrons, with some protons and electrons (d) we have no idea 34. Hawking radiation is emitted by a black hole when: (a) the black hole rotates quickly. (b) the black hole accretes material. (c) avirtualpairofparticlesiscreatedfromthevacuumofspace. (d) synchrotron radiation is emitted by infalling charged particles. 35. The Hubble constant, H0, represents: (a) the rate of expansion of the universe. (b) the speed at which galaxies are moving away from us. (c) the time it takes a galaxy to move twice as far away from us. (d) the size of the universe. 36. Detection of solar neutrinos confirms that: the Sun’s (a) core is powered by proton-proton fusion. (b) transport by radiation occurs throughout much of the solar interior. (c) magnetic fields are responsible for surface activity on the Sun. (d) convection churns the base of the solar atmosphere. 8 37. The event horizon of a black hole is defined as: (a) the point of maximum gravity. (b) the radius of the original neutron star before it became a black hole. (c) the point at which shock waves emanate from the strong gravitational distortion the black hole creates in the fabric of spacetime. (d) the radius at which the escape speed equals the speed of light. 38. Most of the luminosity from the sun is emitted from the: (a) Corona (b) Chomosphere (c) Photosphere (d) Solar Wind 39. If you measure the average brightness and pulsation period of a Cepheid variable star, you can also determine its: (a) age. (b) distance. (c) rotation period. (d) mass. 40. The Collapsar model explains: (a) The formation of white dwarfs (b) The formation of magnetars (c) The formation of neutron stars (d) The formation of some gamma ray bursters (e) none of the above 41. Stars leave the main sequence when (a) They start burning helium in their cores (b) They ascend the red giant branch (c) They run of of hydrogen in their cores (d) They start burning hydrogen in a shell 42. Neutron stars are produced by (a) Type Ia supernovae (b) core collapse of the iron core of a massive star (c) novae on carbon/oxygen white dwarfs (d) CNO burning in solar-type stars 9 43. The equivalence principle says that: (a) being stationary in a gravitational field is the same as being in an accelerated reference frame. (b) the universe is homogeneous and isotropic. (c) at any radius inside a star, the outward gas pressure must balance the weight of the material on top. (d) mass and energy are interchangeable, and neither can be destroyed.